Communication technology developments in the last decade have demonstrated what seems to be a migration from parallel data input/output (I/O) interface implementations to a preference for serial data I/O interfaces. Some of the motivations for preferring serial I/O over parallel I/O include reduced system costs through reduction in pin count, simplified system designs, and scalability to meet the ever increasing bandwidth requirements of today's communication needs. Serial I/O solutions will most probably be deployed in nearly every electronic product imaginable, including IC-to-IC interfacing, backplane connectivity, and box-to-box communications.
While serial interfaces generally offer higher clock rates through the use of, for example, point-to-point connection and low-voltage differential signaling, serial interfaces are nevertheless sensitive to reflections and crosstalk. Furthermore, the appetite for higher clock rates necessarily demands higher slew rates, which exacerbates these problems. As a rule of thumb, for example, the slew rate, which is also referred to as edge-rate or rise time, may generally be designed to be approximately ⅓ of the data bit's cycle time. Thus, for a 1 gigabit-per-second (Gbps) data rate, the cycle time for a single bit is one nanosecond, which according to the rule of thumb, suggests a 333 picosecond edge rate. Similarly, for a 10 Gbps data rate, a 33 picosecond edge rate is required to fall within the rule of thumb design constraint.
As the desirability and popularity of serial I/O interfaces continues to grow, so does the number of communication protocols that are created to use them. As each communication protocol is developed, however, legacy support for the older communication protocols is also required. Thus, the designer is increasingly challenged to deliver a more robust design, which may be used to accommodate not only the newer communication protocols, but also the legacy communication protocols as well.
Designing and validating these robust designs often introduces the designer to physical and electrical design complexities that have not been addressed or even understood before. Conventional design techniques become increasingly inadequate, since the architectures used to model the conventional designs are themselves becoming antiquated. Thus, efforts continue to aid the designer with the daunting task of meeting today's communications needs, while also accommodating legacy communication architectures that are still in use.